Members of the House Armed Services Committee will look into the military and national security impact of the recent data breach at the Office of Personnel Management, calling the reports so far "staggering and unacceptable."
Federal officials acknowledged last week that Social Security numbers, health records and even fingerprints of 21.5 million federal employees — including potentially millions of military personnel — were included in a massive data theft last month.
The agency director resigned a day later.
Rep. Mac Thornberry, R-Texas, the committee chairman, said he and his colleagues are concerned with the potential damage to the Defense Department's military and civilian workforce, and will hold hearings and briefings in coming weeks to look into the problem.
"We have an obligation to ensure that those who serve the department, in or out of uniform, are able to do so securely," he said in a statement.
Thornberry said he is "far from convinced" that OPM has done enough to respond to the breach, either in mitigating the impact of the stolen information or preventing similar theft in the future.
Hearings on the issue likely will begin this fall, after the August congressional recess and after the committee has wrapped up work on the 2016 defense authorization bill. Thornberry said he wants to explore "larger questions of cyber defense and the security clearance process" as part of the investigation.
"From extensive backlogs to colossal breaches, the time to debate and reform OPM's role in the security clearance process has come," he said.
In June, OPM confirmed that hackers had broken into a database housing background investigations on all current, former and prospective federal employees seeking security clearances over the past 20 years.
The breach affected security clearance applicants and nearly 2 million spouses and partners, officials said.
Federal officials have promised to provide credit monitoring and other security measures to affected individuals.